1. Field of the Invention
The present invention relates to rotary web converting machines and more particularly, to rotary cutting devices for paper envelope forming machines.
2. Description of the Prior Art
Business and packet envelopes are formed from a single rectangular sheet of paper wherein the corners have been cut away to leave four peripherially radiating tabs around a rectangular face body. Three of the tabs are folded along perpendicular lines to a flat position adjacent the inside face of the envelope body where they are adhesively secured together to form the envelope pocket. The fourth tab remains unsecured for closing after the envelope contents have been inserted.
In the mass production of such envelopes, the forming corner cuts may be accomplished by means of a batch cutting die or a high speed line series through one or more rotary knives.
By either cutting means, a considerable time and tool investment is required to accommodate all the envelope styles in use and several size permutations of each style.
In the case of batch cutting dies, a different die is required for each size of each style and will cut a stack of approximately 500 blank sheets in a single stroke of a 60 to 90 second press cutting cycle. Style or size changes are implemented by changing the cutting die that is mounted to the cutting press platen. Such die changes require two to four machine hours.
Rotary knives are productively faster, having a production rate in the order of 2000 envelopes per minute but style or size changes require greater machine down time: from eight to sixteen hours. Each rotary cut is executed by a pair of meshing die or knife edges mounted on respective bed rolls. An extremely hard steel die is secured to one roll and a softer steel die is secured to the other. Both dies are arced to the radius of the respective bed roll and correspondingly profiled so that the desired cut profile is sheared from a sheet of paper positioned between the rolls as the two dies close in rolling convergence. Since it is virtually impossible to manually grind two rotatively meshing profiles to the required accuracy, misalignment is accommodated by grinding and mounting the respective dies as well as possible and then non-productively running the machine to operationally lap the two die edges together.
Reference is given to U.S. Pat. No. 3,143,022 for a more complete description of rotary cutting design and operating principles.
Pursuant to the prior art, it was necessary to repeat these complex die mounting and lapping procedures for each envelope style and size change to be effected on a given machine. Consequently, extremely large orders and long production runs of a single style and size were required of rotary machines to achieve a unit cost parity with press die production: notwithstanding that rotary machine operating productivity is considerably greater than batch die cut production.
It was an objective of the present invention, therefore to devise a rotary envelope cutting machine having a rapid style and size change capacity.
Another objective of the invention is to provide a means for changing the style and size of a rotary envelope cut without disturbing the meshing lap of a cooperative rotary knife set.
Another objective of the invention is to teach means for laterally adjusting the lateral cutting depth of a rotary knife set without disturbing the meshing lap between respective knives of the set.
Another objective of the invention is to provide means for micro-adjusting the lap of a rotary knife set to accommodate wear loss without disturbing the original mount position of either knife.
Another objective of the invention is to provide means for selectively adjusting the relative rotational timing of a plurality of rotary cutting knife sets in a production line series without disturbing the meshing lap of a cooperative knife set.
Another objective of the invention is to provide means for selectively adjusting the timing of a lateral cut pair of rotary knife sets relative to another such pair in a production line series without disturbing the meshing lap of any cooperative knife set or the relative timing of respective knife sets within a cooperative pair of knife sets.
Another objective of the invention is to provide means for close order control of small angle relative timing adjustments between two rotary knife sets in a commonly driven pair of knife sets.
Another objective of the invention is to teach a method of rotary envelope cutting whereby a plurality of envelope styles and a reasonable size range within each style may be cut and changed between styles and sizes without disturbing the meshing lap of any of several knife sets.